Requiring it is more convenient for the users. I know that I'm always trying to be safer by using different passwords for different sites. However, if I stop using a site and come back a year later, I probably won't remember my password and it's also possible that I won't remember my user name. Not being able to retrieve this information would discourage me from using the service.
I'm sorry, I read the title very quickly and misread it. My opinion on the actual question is that I generally like it when the log in is the email address and there is a separate display name. This way the username is easy to remember, but the email address remains private.
Comments
Requiring it is more convenient for the users. I know that I'm always trying to be safer by using different passwords for different sites. However, if I stop using a site and come back a year later, I probably won't remember my password and it's also possible that I won't remember my user name. Not being able to retrieve this information would discourage me from using the service.
I'm sorry, I read the title very quickly and misread it. My opinion on the actual question is that I generally like it when the log in is the email address and there is a separate display name. This way the username is easy to remember, but the email address remains private.